It is often desired to concentrate a liquid mixture or solution by removing a portion of the solvent therefrom, leaving the mixture in a more concentrated form. It has been common to concentrate aqueous mixtures such as orange juice, grapefruit juice, grape juice, tomato and other fruit and vegetable juices by evaporation of a portion of the water content. In general, the removal of water from a mixture by evaporation requires substantial energy, since the latent heat of vaporization of water is large. Further, when the evaporation is carried out at elevated temperatures, as is most common, scaling and increased corrosion of the equipment are produced. In addition, with some products, notably fruit juices, heating of the mixture either drives off volatile flavor constituents or otherwise adulterates these materials, thus creating an adulterated or cooked flavor in the final product.
Because of the above-described shortcomings associated with evaporative concentration, it has been found advantageous to freeze concentrate many products, particularly those having water as the liquid carrier. Generally, reduced energy is required since freeze concentrating relies on the latent heat of fusion of water, which is much less than its latent heat of evaporation. In a freeze concentration process, water is removed by cooling the mixture to produce ice crystals, which are separated from the concentrate. As water is removed by freeze concentration, however, the freezing point of the remaining liquid phase becomes increasingly depressed because of the rising solids concentration, thus requiring lower freezing temperatures. In addition, the viscosity of the remaining liquid increases, thus making the separation and washing of the ice crystals increasingly difficult and expensive.